1. Field of the Invention
The present invention relates to a semiconductor light emitting device of an edge emitting type used in an optical interconnection, etc.
2. Description of the Related Art
In the semiconductor light emitting device of an edge emitting type, a cleavage plane is generally used widely as a light emitting surface. Since the cleavage plane is basically a smooth mirror in an atomic order, it is very effective to use the cleavage plane as a light emitting surface. However, it is difficult to form cleavage without any fragments and damages. Accordingly, the formation of cleavage causes problems in view of mass production and yield.
Therefore, the formation of a light emitting surface using etching in stead of cleavage has recently been searched. In the formation of a light emitting surface using etching, light emitting surfaces can be formed together with respect to all light emitting elements within a substrate. Therefore, the formation of a light emitting surface using etching has features of mass production and high yield which cannot be obtained in a cleavage method. Recently, smoothness of this light emitting surface is not inferior to that of the cleavage plane. In the following description, general examples of the semiconductor light emitting device having a light emitting facet formed by etching will next be described.
FIG. 1 is a view showing one example of a general etching mirror semiconductor laser (see Japanese Patent Application Laying Open (KOKAI) No. 3-30381). In FIG. 1, reference numerals 1, 2 and 3 respectively designate an n-type InP substrate, an n-type InP clad layer and an undope-InGaAsP active layer. Reference numerals 4, 5 and 6 respectively designate a p-type InGaAsP guide layer, a p-type InP clad layer and a p-type InGaAsP contact layer. Reference numerals 7, 8 and 9 respectively designate an n-type electrode, a p-type electrode and an etching facet as a reflecting mirror. In the semiconductor laser of FIG. 1, a thickness as a sum of thicknesses of the active layer and the guide layer is set to 0.3 .mu.m so that a reduction in facet reflectivity caused by a slight inclination of the etching facet 9 is restrained to the utmost. It should be understood from FIG. 1 that the InP substrate 1 is projected forward from the etching facet 9 and a light emitting surface and an element facet form a step. This construction constitutes common structural features in the edge emitting type semiconductor light emitting device having a light emitting surface formed by etching.
FIG. 2 is a view showing one example of an optical semiconductor device in which an optical semiconductor element is adhered to a submount (see Japanese Patent Application Laying Open (KOKAI) 2-137389). In FIG. 2, reference numerals 10, 11 and 12 respectively designate the optical semiconductor element, the submount and a stem. Reference numerals 13, 14 and 15 respectively designate a metallized electrode, a light emitting point and a solder material. As pointed out in this laid-open patent, when an obstacle such as a solder material exists in front of the light emitting point 14, light emitted from the light emitting point is scattered. Similarly, there is a case in which phenomena such as light reflection, scatter, interference, etc. are caused with respect to a substrate surface in front of an etching facet described with reference to FIG. 1.
FIG. 3 is a view showing another example of the semiconductor light emitting device having a light emitting facet formed by etching (see Japanese Patent Application Laying Open (KOKAI) No. 5-136459). In FIG. 3, reference numerals 16, 17 and 18 respectively designate a substrate, a light emitting diode array of an edge emitting type and a light emitting layer (an active layer). Reference numerals 19 and 20 respectively designate a p-side electrode and an n-side electrode. In the present invention, a substrate shape in front of a light emitting surface is stepwise formed such that the following geometric relation is satisfied. EQU L X2&lt;L Z2/tan .theta.; (L X2.noteq.L Z2/tan .theta.), (0.degree..ltoreq..theta..ltoreq.90.degree.) EQU L X1&lt;L Z1/tan .theta.; (L X1.noteq.L Z1/tan .theta.), (0.degree..ltoreq..theta..ltoreq.90.degree.)
Therefore, no light emitted from the light emitting facet is interrupted on a terrace surface so that light utilization efficiency is increased.
FIG. 4 shows a semiconductor light emitting device 101 having a structure in which a substrate surface 106 is formed in front of a light emitting surface 107. In this semiconductor light emitting device 101, when light emitted from the light emitting surface 107 is reflected on the forward substrate surface 106, light reflected on the forward substrate surface 106 is interfered with the light emitted from the light emitting surface 107. Therefore, a light emitting direction is inclined several degrees upward on a substrate side. When such a semiconductor light emitting device 101 is connected to an optical fiber 103, optical coupling efficiency to the optical fiber 103 is greatly reduced since a light receiving angle of the optical fiber 103 is small even when the light emitting direction of the semiconductor light emitting device 101 is inclined several degrees. For example, a total light receiving angle of the optical fiber 103 is equal to 23.degree. when a numeral aperture NA is equal to 0.2.
FIG. 3 shows a structure for reducing influences of this interference. In the actual semiconductor light emitting device, a far-field emission pattern also extends on a wide angle side so that it is difficult to completely remove the influences of this interference.